Ethanol can be produced from grain-based feedstocks (e.g. corn, sorghum/milo, barley, wheat, soybeans, etc.), from sugar (e.g. from sugar cane, sugar beets, etc.), and from biomass (e.g. from cellulosic feedstocks such as switchgrass, corn cobs and stover, wood, or other plant material).
Biomass comprises plant matter that can be suitable for direct use as fuel/energy source or as a feedstock for processing into another bioproduct (e.g., a biofuel such as cellulosic ethanol) produced at a biorefinery (such as an ethanol plant). Biomass may comprise, for example, corn cobs and stover (e.g., stalks and leaves) made available during and/or after harvesting of the corn kernels, fiber from the corn kernel, switchgrass, farm or agricultural residue, wood chips or other wood waste, and other plant matter. In order to be used or processed, biomass is harvested and collected from the field and transported to the location where it is to be used or processed.
In a biorefinery configured to produce ethanol from biomass, such as cellulosic feedstocks as indicated above, ethanol is produced from lignocellulosic material (e.g. cellulose and/or hemi-cellulose). The biomass is prepared so that sugars in the cellulosic material (such as glucose from the cellulose and xylose from the hemi-cellulose) can be accessed and fermented into a fermentation product that comprises ethanol (among other things). The fermentation product is then sent to a distillation system, where the ethanol is recovered by distillation and dehydration. Other bioproducts, such as lignin and organic acids, may also be recovered as co-products. Determination of how to more efficiently prepare and treat the biomass for production into ethanol depends upon (among other things) the form and type or composition of the biomass.
One costly step in the preparation of lignocellulosic material for fermentation is the pretreatment of the biomass material, which requires the usage of a suppressed pH in order to degrade the cellulose to sugars. Typically, large doses of acid are utilized to bring the pH of the biomass to the levels required to effectively separate C5 sugars from the C6 solids. The volume of acid required for a commercial scale cellulosic ethanol plant can be very large, which is costly to purchase and store. Further, the large quantities of acid must be subsequently neutralized prior to downstream processing, such as fermentation. Neutralization is also associated with a significant cost, and may result in an excess of minerals, which can buildup in downstream systems.